1. Field of the Invention
The present invention relates to a method of and an apparatus for detecting a defect and a portion having a different-hardness in a test object which has a plurality of protrusions, and more particularly to a method of and an apparatus for detecting which of a plurality of protrusions of a test object has a defect and/or different-hardness therein.
2. Prior Art
Many automotive components are formed by castings. If these components have defects such as cracks, cavities, recesses, or the like, the components tend to be destroyed in use. Any defective components should preferably be detected and rejected from the production line before the components are assembled into automobiles. Detection of the positions of defects in components is helpful in determining the cause of the defects.
If a defect-free cast-iron component has a localized spherical mass of graphite in the cast-iron structure, and the graphite mass is harder than the rest of the component, then a crack or a cavity tends to develop from the harder graphite mass while the component is in use. Components with such localized portions of different hardness should also be rejected from the production line.
Various nondestructive testing methods are known for detecting those defects in engine components. For example, engine component deficiencies have been detected by an ultrasonic echo method, an acoustic emission method which detects a sonic energy wave caused when a crack is produce in a component, a CCD camera image observation method, a radiographic method, and a visual-optical method using a color check, among others.
There have been available many non-destructive processes for determining whether there is a different-hardness mass in a test object.
The ultrasonic echo method uses a transducer or sensor for transmitting and receiving ultrasonic energy into and from a test object. In use, the sensor is held in contact with the test object. Since, however, the ultrasonic energy is propagated linearly through the test object, only the area of the test object which is contacted by the sensor can be tested at a time. The waveform of the ultrasonic energy received from the test object tends to vary due to reflections caused by inadequate coupling between the sensor and the test object or due to slight changes in the angle of the sensor with respect to the test object. Consequently, it is not easy to achieve proper determination of defects in test objects.
The acoustic emission method also employs a sensor held in contact with a test object. Inasmuch as a crack is detected on the basis of an acoustic emission signal produced when the crack is caused, a crack can be detected only while the crack is being developed. Difficulty arises in this testing method unless the a crack to be detected is increasing in a test object.
The CCD camera image observation method is liable to detect discolored spots and patterns other than real defects and is not effective to detect cavities known as blowholes in castings. It is impossible to detect the position of a defect in a test object, using a CCD camera.
The radiographic method allows the operator to make a visual inspection of the internal structure of a test object. However, it is cumbersome to regulate the dose of X-rays to be applied to a test object. A crack in a test object may not be observed if the dose of applied X-rays is not properly regulated.
Since this method has been unable to detect any different-hardness portion in a test object, products with different-hardness regions cannot be rejected from the production line.
If test objects have a plurality of protrusions, each protrusion has to be inspected. It would be timeconsuming and cumbersome to test all test objects with protrusions that needed to be tested. Any conventionally available test method for inspecting test objects with protrusions are suitable for inspection on production lines.